Patent GB-731204-A (GB)
Title: Group selector circuit arrangement for automatic telephone exchanges
IPC: H04Q3/00
Filed: 1953-03-23
Abstract: 731,204. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. March 23, 1953 [March 21, 1952], No. 7980/53. Class 40 (4). Incoming lines belonging to different routes T1 . . . T6 are connected to selectors a1 . . . a9 . . . h1 . . . h9, Fig. 2, and the lines are divided into groups, each containing lines from several routes and having access to links, calls being completed over their appropriate selectors and one of the links, at least one group having links individual to it and used for connections between lines of the same group and also having links shared with other groups. The links are connected to a cross-connecting field MK which may be suitably wired as shown in Fig. 3. First choice lines are connected to selectors whose links are wired to row A and so on, selectors for last choice lines being wired to row H. Links having no cross-connections are used for connections between lines belonging to the same group. Connections between lines of two different groups may be effected over links common to the two groups. Thus a line in group B will first attempt to find a connection in a required direction over links common to A and B, then over links individual to B, then over links common to A, B and C and so on and finally, if the connection cannot otherwise be established, over links common to ABC . . . H. Detailed operation. A call on the incoming line L1, belonging to route T2, operates its line relay TA211 and TA212 follows. The line is connected in known manner, over finder RS to the register REG which receives the incoming digits and, if a call to a line in the route T6 is required, closes its contact 3. The register then operates the chain relay MS1 which connects up the marker M and operates the route relay RT6 over contact 3 of the register. Relay MS1 also brings up BA1 which designates the group to which the calling line belongs. BA1 operates RA2. Each relay of the test chain VL12 ... VL22 corresponds to one of the links and the operation of BA1 connects the upper windings of the test relays associated with the links accessible to the group to leads such as SA. The leads are connected to all the busy contacts (e.g. 137) of all the lines of all the groups to which the link in question has access. The test circuit is completed only for those lines in the wanted direction by contacts of RT6. If a link is busy its test circuit is opened by a relay such as VL11. One only of the test relays VL12 . . . VL22 operates and so selects the first free link capable of connecting a line in the group represented by BA1 to a free line in the traffic route represented by RT6. Suppose VL12 operates indicating link m11. VL12 brings up VL0 and GR follows. The chain VT11 ... VT21 is now operated to determine a free line, within the traffic group designated by RT6, which is accessible to the link m11. Suppose VT11 operates, designating, in combination with RT6, the line L2. VT11 brings up VT0, and also, in combination with RT6 brings up RB2 designating the line group to which the selected line belongs. VL0 in association with VL12 and RA1 operates the pair of select magnets SB1, S10 associated with the link m11; and in association with VL12, RA1, RA2 and RB2 over a circuit including the m1 1 portion of the cross-connecting field MK it brings up the pair of select magnets SB2, S20 associated with the link m11. SB2 brings up the hold magnets AM21, BM61 which hold to TA212 and the connection is now completed oyer m11. AM21 releases the register and marker and the select magnets follow. If m11 is busy, when BA1 operates VL11 comes up over a hold magnet contact, thereby opening the operating circuit for VL12 and another relay of the chain operates to seize another suitable free link.